290 THE AMERICAN MONTHLY [Nov 
deria. There are two forms of petioles, the one short and 
inflated, the other tapering from the base upwards with- 
out special enlargement and reaching sometimes a length 
of 67 centimetres. Both may occasionally be found on 
the same plant. The rhizomes and runners by means of 
which this plant multiplies so rapidly, have a central 
solid part and, around this, numerous air-ways without 
diaphragms, ; 
Fig. 9 shows an inflated petiole a fourth the actual size. 
Figs. 10, 11, 12, 13 give half the real size of successive sec- 
tions of-a tapering cone that was 26 c. m. long, 10 being 
taken at the base and the others at the respective heights 
of 7.6, 15, and 23 c.m. The diaphragms in Hichhornia 
are like fig. 3, but the appertures are much smaller. 
The Sagittaria variabilis of the Northern States and S. 
lancifolia of the South have diaphragms of a somewhat 
different type, the branches of the cells being much more 
numerous and many of the perforations having a long 
oval form. One of these plates is represented in fig. 14, 
enlarged 150 times. It will be observed that of the lines 
formed by the joining of the cell branches only two abut 
on each of the oval openings. Fig. 15 shows half the 
size of a petiole in cross section, taken half way up, in 
which were counted over 400 air-passages. 
The flower-bearing stem of these plants has no large 
central hollow. In the sheathing petioles of the little 
Alisma plantago, which is of the same natural order as 
Sagittaria, the ethmoids are of an intermediate character, 
the cells having from six to twelve branches and there be- 
ing only occasionally an oval aperture between the tri- 
angular ones. The flower-bearing stem is hollow and 
there are some ethmoids in the large cavity. 
Of a still different type are the horizontal partitions 
in the leaves of Typha latifolia. Here they are made up 
of very slender, branching cells and the apertures are 
relatively large and very irregular in form. These aper- 
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